Sound receiver



Patented Oct. 1, 1935- UNITED STATES PATENT orrlca (Granted under theact of March 3,1883, as amended April so, 1928; 3'10 o. e. 757) Aprimary object of the present invention has been to devise a soundreceiver which is reliable and uniform in action and one which may bereadily regulated. A controlling factor in the design of the presentnovel form'of sound receiver has been the need for the matching ofaplurality of such receivers. It has long been recognized in connectionwith the use of hydrophones and similar devices for the reception ofsounds in marine signalling and related fields that one of the greatestdifliculties in the way of accurate determinations, especially inbinaural reception, has been with respect to the matching of soundreceivers.

In the past it has been the general practice to employ microphones toreceive the sound waves due to the extreme sensitivity of these devices.Microphones, however, as is well known, are extremely difiicult to matchand even when matched will not remain matched for any length of time. I

In recent years the practical development of vacuum-tube amplifierswhich are satisfactory for use in connection with binaural reception,makes it possible to employ a receiver which is less sensitive than themicrophone. The present invention has reference to a receiver of thistype, which is non-microphonic and is therefore of lower sensitivity butwhich has a correspondingly greater uniformity of action. For thispurpose the device embodying the invention is based upon the principleof the magneto-phone and a primary feature is in the development of aninstrument of this type having a, balanced armature.

The armature contemplated by the present invention is placed under theinfluence of a plurality of distinct magnetic circuits sohrarranged anddirected that the summation of their forces on the armature when it isat rest is zero. The

construction is such, furthermore, that when the armature is displacedfrom its neutral position, as by means of a diaphragm; onlycomparatively weak restoring forces will be brought into play and thenatural or resonant frequency of the armature can be kept below therange of the sound spectrum that it is desired to receive. Theimportance of providing a natural or resonant frequency of the armatureoutside of the range of sounds to be received will be readily apparent.Both the intensity and phase relations of the vibrations of any type ofsound receiver change very rapidly for frequencies near the resonantfrequency of the receiver. For this reason it becomes highly necessaryin the matching of receivers to so design them that their resonancefrequencies fall either aboveor below the range that is to be received.The difficulty with adopting a natural frequency above the range to bereceived is that excessively large restoring forces 5 will be requiredwith the consequent reduction in sensitivity of the receiver. It willtherefore be clear that the balancing of the armature by means of theopposed normal'magnetic forces is an'important feature of the presentinvention. 10 I Another advantageous feature which may be mentioned isthe simplicity of construction which is such as to permit themanufacture of the major portions of the device from stampings. This notonly gives rise to ease of manufacture but pemiits more. readily thestandardization of the units. Incidental and more specific objects andadvantages of the invention will be apparent from the detaileddescription which follows and which is to be considered in connectionwith the accom- 20 panying' drawing.

In the drawing:

Figure 1 is a plan view of the assembled sound receiver,

Figure 2 is a. cross sectional view of the receiver taken along adiameter-line of Figure-1, and shows in addition one form of circuit.which may be employed, and

Figure 3 shows a modified construction of the device and anothersuitable form of circuit. 30 Referring particularly to Figure 2, thereis shown a cylindrical casing I which maybe made of any suitable'material, preferably a non-con.- ductor of electricity as well asmagnetic lines of force, such as a phenolic'condensation product. Aflange formed at the bottom of this cylindrical casing serves ,toprovide. a seatJor a disk! which has an aperture therein adapted topermit-the free passage of a core I. Formed as a unit with this core isa large disc .4, preferably made of 9 transformer steel, and which is ofsuch diameter as to be capable of free movement within the casing. A.cylindrical nut 5, having an outside diameter equal to that-of the core3, serves to 7 hold the. three elements a, 4, and s, rigidly as a unit,and at the same time serves as a core equivalent to the core 3 on theopposite side of disc 4. It will be apparent that this construction isadopted primarily. for-the purpose of permitting easeiof assembly andthat any one of a number of other suitable ways might be adopted forproviding a unit similar to that formed by the elements 3, 4 and 5. Thisunit will be referred to hereinafter as an armature.

Toward the upper end of'the cylindrical casing, there is inserted a disc6 which is similar to the lower disc 2, and has an aperture adapted topermit the free passage of the element 5. An

annular ring 1 has a screw-threaded connection with internal threads atthe upper end of the casing, and is for the purpose of holding the partstogether as well as adjusting the normal relation thereof. Between thedisc 6 and the armature disc 4, and surrounding the element 5,

is an annular coil 8 of wire of any suitable material preferably a goodelectrical conductor. A second annular coil 9 is mounted on the outsideof coil 8 and serves as a secondary winding. A similar arrangement ofannular coils lflzand II is provided between the disc 2 and the armaturedisc 4. Between the element 5 andthe.

inside of coil 8, there is provided a series of thin annular members l2,consisting preferably of laminations of transformer steel. On theoutside of coil 9, between its periphery and the inside of casing I,there is arranged a similar series of annular members or laminations I3.A similar construction comprising the two series of annular members orlaminations "and I5, is provided between the discs 4 and 2. It will beapparent that the several series of laminations I2, l3, l4 and I5, serveto provide circuits for a magnetic flux which will surround and passthrough the several coils. A stem I 6 projecting from the core 3, may beconnected in any suitable way to a diaphragm l1 that is adapted toreceive impulses from sound or similar waves to be detected by'the novelmeans disclosed.

In the operation of the device, a battery l8. or other suitable D. C.source of electricity, is connected in series or parallel with the twoinner coils 8 and I0. The turns of these coils are preferably wound insuch sense, one clockwise and the other counter-clockwise, about thecore elements as to set up opposed magnetic fields. Thus the current maybe made to fiow in the two coils in such a direction that a north polewill be established toward each of the two outer ends of the device.This particular arrangement of the coils is not essential however sincethe important feature is that the two magnetic fields thus establishedshall exert opposite pulls upon the armature disc I so that the latterwill normally assume a condition of balance between these opposiingforces. We may assume that the lines of the upper magnetic field travelthrough the circuit established by the disc 6, laminations l2, armature4, and laminations l3, while the lines of the lower magnetic field maybe assumed to travel through the circuit comprising disc 2, laminationsM, armature l, and laminations l5.

Now it will be apparent that if a sound wave strikes the diaphragm II toforce the core 3 and armature 4 upwardly, as shown in Figure 2,

the laminations l2 and I! will be compressed so that the air gapsbetween these members will be reduced, and consequently the fluxthreading the upper magnetic circuit will be increased. On

the other hand. the laminations "l4 and I! will be extended due to theirresilience so that the air gaps between these members will be increased,causing a corresponding increase in the reluctance of the lower magneticcircuit and a decrease in the flux threading this circuit.

' result which is to be noted in connection with this displacement ofthe armature; is that the attraction created by the upper magnetic field75. for the armature will be increased, while the One attraction of thelower magnetic field for the armature will be decreased, so that therewill be a tendency to further upset the balance which previouslyexisted. However, all of the laminations l2,-l3, l4 and iii are, asstated, preferably made of steel so that they have considerableresilience. It will be apparent, therefore, that the force differentialcreated by the unbalanoing of the magnetic field will be opposed by anelastic force of the Iaminations which have been com- 10 pressed. Thiselastic force will preferably approximate as nearly as possible but beslightly greater than the unbalanoing magnetic forces so that there willalways be a tendency to centralize the armature. In this way, thecentrall5 izing or restoring forces will be relatively small so thatthey will interfere only slightly with the movements imparted' by thediaphragm. The obvious advantage of this construction is increasedsensitivity. 20

Considering now the electrical effects which will be produced by theassumed movement of the armature it will be apparent that the variationsin the magnetic flux passing through the coils 9 and II will tend toinduce current in 25 these coils. Thus the increase in flux through thecoil 9 will tend to induce therein an E. M. F. which will oppose theincrease. On the other hand the decrease in flux through the coil IIwill induce an E. M. F. therein which will tend 30 to oppose thedecrease. Now by suitably connecting the terminal wires of the coils 9and H they may be coupled in series in such a way as to add 'the two E.M. F.s induced. The 118088. sity for the employment of the secondarycoils 35 9 and II instead of relying solely on the primary coils inconnection with the series arrangement shown in Figure 2 will beapparent when it is considered that the induced effects in coils 8 andIll 'due to the movement of the armature 40 will be in oppositedirections and if equal will produce no net results whatever. The E. M.F. induced ,in coil 8 in opposition to the current from the battery It!be offset by the E. M. F. induced in coil III in a direction to aid thiscur- 45 rent.

One way of insuring the proper connection between the coils 8 and H foradding their effects may be as follows: The coil 9 may have its windingsin opposite sense to the windings of the coil 8 so that the currentinduced in coil 9 will be in the opposite direction from the change ofE. M. F. in coil 8, and under the conditions assumed will therefore beinthe directionof the current from the battery l8. Now, if coil ll 55wound in the same sense as coil III the current induced therein will bein the same direction as the change .of E. M. F. in coil it which, underthe conditions assumed, will also be in the direction of the currentfrom battery It. The reverse 60 movement of the diaphragm and armaturewill of course produce directly opposite effects in the two coils sothat an alternating current will be induced so long as the diaphragm isvibrated.

These combined induced currents in coils 9 and 5 ll may be-led through aprimary coil IQ of a transformer whose secondary coil 20 is in circuitwith any suitable means for providing a visible or audible indication,such as a galvanometer or a telephone receiver 2|. It will be'obviousthat any 70 the event that the currents directLv induced are too smallto produce the desired effects. The

transvi rmer [S 20 maybe omitted if theourrents J5 induced in coils 9and II aresuflicient to operprecisely the same as shown in Figure 2} Thecoils 8' and III which correspond respectively to coils 8 and ID of thefirst described construction are connected in parallel with a D. C.source of electricity and are wound in such sense asto establishopposite magnetic fields acting upon the armature 4. One branch of thecurrent from the D. C. source, such as a battery It, passes through thecoil 8' and then through a primary coil 22 of a transformer A. Anotherbranch of the current will flow through the coil l and then through aprimary coil 23 of another transformer B. Movements of the armature 4will, as in the first case discussed, produce variations in flux throughthe two magnetic circuits threading the coils 8' and I 0'. As the fluxthrough coil 2' is increased there will be a change in the currentthrough the primary coil 22 by virtue of an. induced E. M. F. in-thisbranch of the circuit opposing that of the source l8. On the other handa corresponding decrease in the flux through coil ill will cause anincrease in the current flowing through the coil 23. These changes inthe current passing through coils 22 and 23 will induce correspondingcurrents in'the secondary. windings 24 and 25, respectively, ofthetransformers A and B and if these secondary coils are properlyconnected in series the two induced currents may be added. Any suitablemeans, such as a gal vanometer 26 or a telephone receiver may beemployed for giving a visual or audible indication ofthe current thusinduced. While the coils 22', 24 and 23, 25 have been referred to asconstituting two separate transformers it .will-be apparent that theymay in reality be separate sections of the same transformer.

While two admirable forms of embodiment of the invention have beendescribed in the foregoing sections, it will be understood that numerouschanges may readily be made in either form within the scope of theclaims which will be hereinafter made. Other materials than thosesuggested may be employed for the various parts of the device. It willbe recognized that an important feature of the invention is in theability.

to control the natural frequency or resonance of the armature byregulating the compression of the laminations i2, l3, l4 and I5 throughthe mere adjustment of the clamping ring I. By the means disclosed it ispossible to materially vary the restoring force and correspondinglychange the natural frequency to hold it below any range to be detectedby the diaphragm IT. The device may be employed in a variety of ways andfor a variety of purposes, being particularly suited to use whereuniformity and precision in action are required.

The invention herein described may be manufactured and used by or forthe Government of the United States for governmental purposes 1armature;

a portion of the magnetic circuit for each of said fields, meansresponsive tosaid mechanical vibrations for compressing part of saidlaminations so as to decrease the reluctance of said portion of one ofsaid magnetic circuits while the re- 5 mainder of said laminations tend.to expand due to their resilience so as to increase the reluctance ofsaid portion of another of said magnetic circuits,'and means coupledwith said magnetic circuits for detecting variations in the reluctanceof said circuits produced by the movements of said 2. In a vibrationdetector a series of coils, a D. C. source of electricity in circuittherewith, magnetic circuits of variable reluctance in-the fields ofsaid coils including a plurality of loosely mounted laminations, meanscooperating with said laminations for compressing certain of saidlaminations while those laminations not compressed tend to expand due totheir'resilience so as to vary the reluctances of said magneticcircuits, and a second series of coils electrically connected in seriesand arranged between said first mentioned series of coils andsaidlaminations, said second series of coils adapted to have currentsinduced therein in accordance with the combined variations in thereluctances or said magnetic circuits.

3. A device for translating mechanical vibra-- tions into electricalenergy comprising a disc-like armature responsive to said mechanicalvibrations, a pair of fiat annular coils disposed adjacent said armatureand on opposite sides thereof, the axis of said coils beingsubstantially coincident with the axis of said armature, means forpassing current through said coils in opposite senses relative to eachother to produce opposed magnetic fields and normally balance saidarmature, andmeans for increasing the flux in one of the magnetic fieldsand simultaneously decreasing the flux in another of the magneticfields, said means comprising a plurality of loosely mounted laminationsarranged on opposite sides of said armature, said laminations beingadapted to. be compressed together first those laminations on one sideand then those on the other side of said armature by the vibrations ofsaid armature, whilethose laminations not compressed tend to separatedue to their resilience.

4. In a device for translating mechanical en-' ergy, a plurality ofcoils adapted .to establish separate magnetic fields, an armaturemounted between said coils, a plurality of loosely mounted laminationsforming a portion of the magnetic circuit for each of said fields, saidlaminations being arranged in two groups on opposite sides of saidarmature, said armature being movable in response to said mechanicalvibrations .for compressing said groups of laminations alter- ,nately,while those not compressed tend to expand due to their resilience,.so asto vary the reluctance of said portions of the magnetic circuits, andmeans coupled with said magnetic circuits for de'tectingvariations inthe fiux produced by the movements of said armature. 5. In a vibrationdetector a plurality of fiat, annular primary coils, a constant D. C;source of electricity in circuit with said coils adapted toproducemagnetic flux in an 'annularpath through said coils, a pluralityof fiat, annular secondary coils mounted concentrically-with saidprimary coils in the magnetic fields of said primary coils, each of saidsecondary coils being arranged in the same plane as one of said primarycoils so as to encircle said primary coil,

magnetic circuits of variable reluctance in the field of said coilsincluding a plurality of loosely mounted laminations arranged -in theplanes of said coils, anda disc-like armature responsive to mechanicalvibrations and mounted between the planes of said coils with its axissubstantially c'oinciding with the axis of said coils, the vibrations ofsaid armature compressing the-laminations on one side whilesimultaneously allowing the laminations on the other side to expand dueto their resilience so as to decrease and increase, respectively, thereluctance of the magnetic circuits on opposite sides of said armature.

HARVEY C. HAYES.

